1. Field of the Invention
The present invention relates generally to a metal gate forming process, and more specifically to a metal gate forming process including at least a metal layer formed by two processing steps.
2. Description of the Prior Art
Poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). However, with the trend towards scaling down the size of semiconductor devices, the conventional poly-silicon gates face problems such as lower performance due to boron penetration and unavoidable depletion effect, which increases the equivalent thickness of the gate dielectric layer, reduces the gate capacitance, and worsens the driving force of the devices. Therefore, work function metals that are suitable to serve as high-K gate dielectric layers are used to replace the conventional poly-silicon gate to be the control electrode.
Therefore, barrier layers and wetting layers are deposited between layers such as work function metal layers to prevent these layers from diffusing to each other and to improve adhesion of these layers.